Abstract: Objective To investigate the regulatory mechanism of miR-451 a on the invasion of human villous trophoblasts. Methods Human chorionic villus trophoblast cell line HTR-8/SVneo was transfected with synthetic oligonucleotide miR-451 a mimics.Reverse transcription-real-time PCR was used to detect the expression of miR-451 a and macrophage migration inhibitory factor（MIF） mRNA.The expression of MIF protein in transfected cells was detected by Western blot.Transwell cell invasion assay was used to observe the changes of cell invasiveness before and after transfection.The recombinant human macrophage migration inhibitory factor（rhMIF） and ISO-1,the specific inhibitors of MIF,were added to HTR-8/SVneo cells.The expression of E-cadherin protein and Vimentin protein in cells was detected by Western blot. Results The level of miR-451 a in HTR-8/SVneo cells transfected with miR-451 a mimics was significantly increased,the expression of MIF mRNA and protein was decreased,and the cell invasive ability was decreased.Compared with the blank group,E-cadherin protein levels were decreased and Vimentin protein levels increased in the rhMIF group,while increased E-cadherin protein expression and decreased Vimentin protein expression were observed in the ISO-1 group. Conclusions Transfection of miR-451 a down-regulates the expression of MIF in human extravillous trophoblasts and may regulate the invasion ability of human villous trophoblast cells through the epithelial-mesenchymal transition pathway.